Type of skin cancer. There 3 main types of skin cancers basal cell carcinoma which rarely spreads, squamous cell carcinoma which arises from the top layers of the skin and can spread and melanoma which arises from the pigment cells. Ssquamous cell carcinomas can start as actinic keratosis, precancerous lesion and then evolve into nosema disease and well to moderately, to poorly differentiated cancer.